Date: Sun, 16 Oct 2016 19:42:55 +0100 From: Gary Palmer <gpalmer@freebsd.org> To: "Eugene M. Zheganin" <emz@norma.perm.ru> Cc: "stable@freebsd.org" <stable@freebsd.org> Subject: Re: zfs/raidz: seems like I'm failing with math Message-ID: <20161016184255.GA2241@in-addr.com> In-Reply-To: <fa71cc53-83f3-2315-d047-36679700dd18@norma.perm.ru> References: <fa71cc53-83f3-2315-d047-36679700dd18@norma.perm.ru>
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On Sun, Oct 16, 2016 at 09:56:10PM +0500, Eugene M. Zheganin wrote: > Hi. > > FreeBSD 11.0-RC1 r303979, zfs raidz1: > > ===Cut=== > > # zpool status gamestop > pool: gamestop > state: ONLINE > scan: none requested > config: > > NAME STATE READ WRITE CKSUM > gamestop ONLINE 0 0 0 > raidz1-0 ONLINE 0 0 0 > da0 ONLINE 0 0 0 > da1 ONLINE 0 0 0 > da2 ONLINE 0 0 0 > da3 ONLINE 0 0 0 > da4 ONLINE 0 0 0 > da5 ONLINE 0 0 0 > > ===Cut=== > > 6 disks 960 Gbs each: > > ===Cut=== > > # smartctl -a /dev/da0 > smartctl 6.5 2016-05-07 r4318 [FreeBSD 11.0-RC1 amd64] (local build) > Copyright (C) 2002-16, Bruce Allen, Christian Franke, www.smartmontools.org > > === START OF INFORMATION SECTION === > Model Family: Samsung based SSDs > Device Model: SAMSUNG MZ7KM960HAHP-00005 > Serial Number: S2HTNX0H507466 > LU WWN Device Id: 5 002538 c402bdac1 > Firmware Version: GXM1003Q > User Capacity: 960 197 124 096 bytes [960 GB] You're confusing disk manufacturer gigabytes with real (power of two) gigabytes. The below turns 960 197 124 096 into real gigabytes % bc scale = 4 960197124096 / 1024 / 1024 / 1024 894.2532 > Sector Size: 512 bytes logical/physical > > [...] > > ===Cut=== > > But: > > ===Cut=== > > # zpool list gamestop > NAME SIZE ALLOC FREE EXPANDSZ FRAG CAP DEDUP HEALTH ALTROOT > gamestop 5,22T 4,38T 861G - 24% 83% 1.00x ONLINE - > > ===Cut=== > > Why 5.22T ? If zpool is displaying raw size, it should be 960 x 6 = 5760 > Gb = 5.65 T. If it's displaying the actual data, then it should be 960 x > 5 = 4800 Gb = 4.68 T. 5.22 T is neither of these. I'm stuck, please > explain. :) Take 6 disks, size calculated above, and turn that into power of two TB: 894.2532 * 6 / 1024 5.2397 Close enough to 5.22, especially after ZFS has some overhead for it's own data structures Regards, Gary
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